The district director for sophomore Democratic Rep. Tony Cárdenas notified the House Thursday that she’s been subpoenaed by a federal grand jury conducting an investigation in the U.S. District Court for the Central District of California.

Gabriela Marquez, who heads operations in the Los Angeles congressman’s Panorama City office, issued the formal notice in accordance with House rules and staff in the congressman’s Washington, D.C., office confirmed the April 13 communication, but did not provide further details.

Sources in California tell CQ Roll Call the FBI spent a few hours interviewing Marquez in her California home roughly three weeks ago, asking questions about whether staffers in Cárdenas’ office worked on campaign-related activities while being paid for official office time.